An Update on F-35 Manufacturing: The Case of Wing Assembly
6/20/2010 SLD visited the Fort Worth assembly plant for the F-35 in late April. During the visit, the focus was upon the transformation of the outer wing box assembly production approach. During the System Development and Demonstration (SDD) phase, wings have been built in the more traditional military aircraft assembly approach of building around stations.
The parts and components come to the station and the wing is assembled over a period of months at the station.
The plant is undergoing change as overhead rail track systems are being installed, after which the outer wings boxes will be assembled using a flow process, rather than a station process. The wing will be assembled by going through two broad flows lines for each side of the wing, with stops along the way at 34 individual stations. Each station does “an individual statement of work” on the wing after which the wing is moved to the next station for the next “statement of work.” Each station within the flow is organized around a work team, which standardizes the effort for that statement of work.
The shift from focus on the stations to flow will enhance production rates and efficiency of the manufactured aircraft, and this is supported by significant capital investment in advanced technologies such as the automated drilling machines seen in the production process today.
The overhead rails should be fully in place by October with the flow process unfolding early next year.The slide show below shows the progress underway.
- The first slide shows a wing in the traditional station approach.
- The next slides show the construction of the overhead rails. After the slides showing the construction of the rails, a wing machine near the overhead rails is pictured.
- And the final slides show a wing entering the overhead rail area.
The tour and interview were conducted by Don Kinard, Technical Deputy for JSF Global Production Operations and lead for Development of the F-35 Fighter Production System. The Fighter Production System was established to facilitate transition from a current 1 aircraft per month production rate to a 20 aircraft per month production rate in 7 years. Prior to this assignment Don was Director of F-35 Production Engineering and held various positions in both Engineering and Manufacturing during his 18 years on the F-22 Program.
What follows are some excerpts from the discussion during the plant visit, which highlights some of the key elements of the shift from the static station to flow process.
SLD: How would you describe the basic difference between the wing assembly approach under SDD and under the production approach?
Don Kindard: I think the basic difference is flows. We are trying to move the product in the wing areas wherever we can. For instance, when we produce one aircraft a day, we want to move the wings from station to station each day. We want to create rhythm in the factory so that everything flows, everything moves at a standard pace all through the factory. That’s the number one thing. So everywhere we can we’ll be moving it with overhead rail systems to get flow on the parts.
SLD: What’s the difference between station and flow?
Don Kindard: Station build is essentially that I move a wing to a station and it stays there for the entire span time of that build. For example, if I had 20 days of span I’d move to a station and stay there 20 days. When I use flow, I have 20 stations but each one of them is doing a standard set of work. The product moves from one station to another in a standard time span.
The advantage of that is that I get the mechanics performing standard tasks in a standard time. They learn much quicker, they do the same thing basically every day. All the parts and tools they need are right there delivered to that point of use for that particular station, so everything is optimized all the way down the line. Ultimately, you will find that you don’t need 20 stations because the work is performed more efficiently and you save labor and facilities costs.
SLD: We are looking at an auto-drilling machine. Tell me the advantage of being able to use this machine in the manufacturing process?
Don Kindard: Here’s a wing auto drill; it drills about 3,500 holes per side of the wing, upper and lower wing. So, 7,000-plus holes, and it drills, reams, and countersinks-the wing and substructure in one step, with essentially perfect quality. The yield on auto drilling about 99.8%, which is amazing compared to manual drilling.
So, for example, the forward fuselage we are looking at takes about two shifts to drill the subassembly. It takes about two weeks to accomplish the same thing on a legacy aircraft.
The wing is very much the same thing. If we didn’t use an auto drill, I’d have all these manual tools (drill templates) that I have to locate on each wing, I’d have to drill them up, then take the wings off, and manually countersink them. This automated equipment does all that in one step. Again, it’s about almost a 10 to 1 difference in span, plus the added benefit of perfect quality.
SLD: We are at a substation where the technician is preparing drawings for the wing subassembly work. Tell me how the digital thread process helps precision and savings of time in this process?
Don Kindard: You’ve heard us talk about digital thread before and this is a perfect example. Again, we take the bulkheads and first thing we do before we load them in the assembly tools is to do as much work at a subcomponent level as we can. So this is an example.
The wing has about 2,000 brackets, which hold tubes, wires and systems. With legacy technology, we would have built individual locating tools, for each of these brackets. The tools would have bumped against a flange of the bulkhead in a particular location to position the bracket.
Using the digital thread, what we do now and what we started doing on F-22 that we transitioned out to F-35, is these bulkheads go to a machine that marks the position of the brackets directly on them using the digital thread. It puts an inkjet mark where these brackets go; it gives you a little outline. I, as the mechanic, take the bracket, apply double-back tape and stick it to the bulkhead using the inkjet marks. The brackets have pilot (undersized) holes for the fasteners. I just transfer those holes into the structure then install the bracket.
So, using the digital thread, I eliminate 6,000 tools, or 2,000 per variant, plus all the time it takes to do configuration management on those tools, plus finding them and getting them to the mechanic. Once again, because of the digital thread, I also eliminate mistakes positioning and locating brackets, which is normally one of our high drivers for quality.
SLD: The composite machine we are standing in front of also suggests an interesting approach to manufacturing which shapes a new way to build a composite wing. Could you describe the approach being followed here?
Don Kindard: I mentioned the key to what we call supportable LO, meaning that the aircraft can go and be Very Low Observable (stealthy) and also very supportable, meaning low maintenance hours for every flight hour. The magic is here in controlling the thickness of the skins. By controlling the thickness of the skins, we’re controlling the mismatch from one skin to the other across the joint. Eliminating those mismatches means less radar reflectivity, which is what a stealth fighter is all about.
Maybe one of the cleverest things that I’ve ever seen in composites – I mean I started in the composites world, and the Holy Grail has always been to build composites to a precisely controlled thickness. One way we do it on most of the other components (forward fuselage, aft fuselage and empennage) is to add sacrificial material to the skins and then we machine it to a nominal thickness with a high-tolerance machine because we’re trying to control thickness plus or minus a particular tolerance, which is tremendously better control than we’ve ever had.
For our wings, we invented and patented a process were we measure the cured wing thickness using a laser radar system, calculate where we need to add material to compensate for the thickness, transfer this data to an automated ply cutter, and then transfer this data to a laser projector, which tells the mechanic where to add the plies. The main benefit is lower capital and facilities cost.
SLD: We are standing in front a wing-skin machine. I see the technician is using the digital thread technology. Could you describe what he is doing and how the technology impacts on the time necessary to do the task, as well the precision of the task?
Don Kindard: This is a wing skin – the outer surface of the wing — and this wing skin would normally have three drawings to put in fasteners on the wing skin. Because it’s all digital technology, he is using a laser to mark down on the wing skin which engineering fastener goes in each hole.
Before we were using the lasers, we were getting out the drawings, which would take us about four days to do this. Now it is much faster. Everything marked on here goes to the final installation area, and the guys don’t look at drawings, they just put in fasteners.
Now, at some point we may end up doing this real-time, fully integrated within production flow, but today it’s much better to do everything off critical path. Now this is only the beginning – you can also do it optically, you don’t have to use lasers. But we can do this in a shift now, when than it used to take us about four days.
***Posted on June 20th, 2010